How do you extrude a shape without outer faces and edges?
This feature has just been added to Blender.
It will be available from version 2.90(https://builder.blender.org/download/).
It's called &quot;Extrude Manifold&quot; and is located in the toolbox T, under the &quot;Extrude&quot; dropdown, Or by pressing Alt+E.

↑ Here I'm using Face select mode (3) but it works in vertex select too